Generally, a touch pad may be linked with a computer through a screen to directly input or output information and detect coordinates of a touched position when a human hand or an object touches a character or a specific location which is displayed on a screen to carry out a specific processing corresponding to a menu of the coordinates selected by software from the coordinates.
Therefore, the touch pad provides a function as an information display unit and a function as an input unit.
Recently, the touch pad using a sound wave has been used. In this case, the sound wave touch pad estimates a position of a finger using a sound wave sensor.
The sound wave touch pad requires at least two microphones to recognize the position of the touch. In this case, to recognize the position using one microphone, a change in energy absorption may be recognized by changing roughness of a surface of the touch pad and vibrating the touch pad in advance.
However, the touch pad using a sound wave according to the related art has a limited recognition effect when there is no rubbing input in the method for using surface roughness. Since multiple knocking frequencies need to be recognized to carry out many commands, a system recognition error may occur, and since the user input and the feedback are not performed, the convenience of use may be degraded.